build: address some -Weverything warnings, update picky warnings

`-Weverything` is not enabled by curl, and not recommended by LLVM,
because it may enable experimental options, and will result in new
fallouts after toolchain upgrades. This patch aims to fix/silence as much
as possible as found with llvm/clang 21.1.0. It also permanently enables
warnings that were fixed in source and deemed manageable in the future.
`-Wformat` warnings are addressed separately via #18343.

Fix/silence warnings in the source:
- typecheck-gcc.h: fix `-Wreserved-identifier`.
- lib: silence `-Wcast-function-type-strict`.
  For llvm 16+ or Apple clang 16+.
- asyn-ares: limit `HAPPY_EYEBALLS_DNS_TIMEOUT` to old c-ares versions.
- curl_trc: fix `-Wc++-hidden-decl`.
- doh: fix `-Wc++-keyword`.
- ftp: fix `-Wreserved-identifier`.
- ldap: fix `-Wreserved-identifier`.
- mqtt: comment unused macro to avoid warning.
- multi_ev: drop unused macros to avoid warnings.
- setopt: fix useless `break;` after `return;`.
- gtls, mbedtls, rustls: silence `-Wconditional-uninitialized`.
- socks_sspi, schannel, x509asn1: fix `-Wimplicit-int-enum-cast`.
- x509asn1: fix `-Wc++-keyword`.
- openssl: scope `OSSL_UI_METHOD_CAST` to avoid unused macro warning.
- libssh2, wolfssl: drop unused macros.
- curl_ngtcp2, curl_quiche, httpsrr, urlapi: drop/limit unused macros.
- tool_getparam: fix useless `break;` after `return;` or `break;`.
  Not normally enabled because it doesn't work with unity.
  https://github.com/llvm/llvm-project/issues/71046
- tool_operate: fix `-Wc++-keyword`.
- curlinfo: fix a `-Wunsafe-buffer-usage`.
- tests: silence `-Wformat-non-iso`.
- lib557: fix `-Wreserved-identifier`.
- lib1565: silence `-Wconditional-uninitialized`.

Enable the above clang warnings permanently in picky mode:
- `-Wc++-hidden-decl`
- `-Wc++-keyword` (except for Windows, where it collides with `wchar_t`)
- `-Wcast-function-type-strict`
- `-Wcast-function-type`
- `-Wconditional-uninitialized`
- `-Wformat-non-iso` (except for clang-cl)
- `-Wreserved-identifier`
- `-Wtentative-definition-compat`

Silence problematic `-Weverything` warnings globally (in picky mode):
- `-Wused-but-marked-unused` (88000+ hits) and
  `-Wdisabled-macro-expansion` (2600+ hits).
  Triggered by `typecheck-gcc.h` when building with clang 14+.
  Maybe there exists a way to fix within that header?
  Ref: https://discourse.llvm.org/t/removing-wused-but-marked-unused/55310
- `-Wunsafe-buffer-usage`. clang 16+. 7000+ hits.
  May be useful in theory, but such high volume of hits makes it
  impractical to review and possibly address. Meant for C++.
  Ref: https://clang.llvm.org/docs/SafeBuffers.html
  Ref: https://stackoverflow.com/questions/77017567/how-to-fix-code-to-avoid-warning-wunsafe-buffer-usage
  Ref: https://discourse.llvm.org/t/rfc-c-buffer-hardening/65734
  Ref: https://github.com/llvm/llvm-project/pull/111624
- `-Wimplicit-void-ptr-cast`. clang 21+. 1700+ hits.
  C++ warning, deemed pure noise.
  Ref: https://github.com/curl/curl/issues/18470#issuecomment-3253506266
- `-Wswitch-default` (180+ hits), `-Wswitch-enum` (190+ hits),
  `-Wcovered-switch-default` (20+ hits).
  Next to impossible to fix cleanly, esp. when the covered `case`
  branches depend on compile-time options.
- `-Wdocumentation-unknown-command` (8+ hits).
  Triggered in a few sources. Seems arbitrary and bogus.
- `-Wpadded` (550+ hits).
- `-Wc++-keyword` on Windows, where it collides with `wchar_t`.
  (100+ hits)
  Ref: https://github.com/llvm/llvm-project/issues/155988
- `-Wreserved-macro-identifier`. clang 13+. 5+ hits.
  Sometimes it's necessary to set external macros that use
  the reserved namespace. E.g. `_CRT_NONSTDC_NO_DEPRECATE`,
  `__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__`, `__NO_NET_API`,
  possibly `_REENTRANT`, and more.
  It's not worth trying to silence them individually.
- `-Wnonportable-system-include-path` with `clang-cl`.
  It'd be broken by doing what the warning suggests.
- `-Wformat-non-iso` for clang-cl.

CMake `PICKY_COMPILER=ON` (the default) or `./configure`
`--enable-warnings` (not the default) is required to enable these
silencing rules.

Also:
- autotools, cmake: fix Apple clang and mainline llvm version translations.
  Ref: https://en.wikipedia.org/wiki/Xcode#Toolchain_versions
- autotools, cmake: enable `-Warray-compare` for clang 20+.
  Follow-up to 4b7accda5a #17196
- cmake: fix to enable `-Wmissing-variable-declarations` at an earlier
  clang version.
- cmake: update internal logic to handle warning options with `+` in
  them.
- cmake: fix internal logic to match the whole option when looking
  into `CMAKE_C_FLAGS` for custom-disabled warnings.

Follow-up to b85cb8cb4e #18485

Closes #18477

lib/ldap.c

@@ -119,30 +119,30 @@ struct ldap_urldesc {
   char   *lud_filter;
 #endif
   char  **lud_exts;
-  size_t    lud_attrs_dups; /* how many were dup'ed, this field is not in the
-                               "real" struct so can only be used in code
-                               without HAVE_LDAP_URL_PARSE defined */
+  size_t  lud_attrs_dups; /* how many were dup'ed, this field is not in the
+                             "real" struct so can only be used in code
+                             without HAVE_LDAP_URL_PARSE defined */
 };
 
 #undef LDAPURLDesc
 #define LDAPURLDesc struct ldap_urldesc
 
-static int  _ldap_url_parse(struct Curl_easy *data,
-                            const struct connectdata *conn,
-                            LDAPURLDesc **ludp);
-static void _ldap_free_urldesc(LDAPURLDesc *ludp);
+static int  ldap_url_parse_low(struct Curl_easy *data,
+                               const struct connectdata *conn,
+                               LDAPURLDesc **ludp);
+static void ldap_free_urldesc_low(LDAPURLDesc *ludp);
 
 #undef ldap_free_urldesc
-#define ldap_free_urldesc       _ldap_free_urldesc
+#define ldap_free_urldesc       ldap_free_urldesc_low
 #endif
 
 #ifdef DEBUG_LDAP
   #define LDAP_TRACE(x)   do { \
-                            _ldap_trace("%u: ", __LINE__); \
-                            _ldap_trace x; \
+                            ldap_trace_low("%u: ", __LINE__); \
+                            ldap_trace_low x; \
                           } while(0)
 
-  static void _ldap_trace(const char *fmt, ...) CURL_PRINTF(1, 2);
+  static void ldap_trace_low(const char *fmt, ...) CURL_PRINTF(1, 2);
 #else
   #define LDAP_TRACE(x)   Curl_nop_stmt
 #endif
@@ -346,7 +346,7 @@ static CURLcode ldap_do(struct Curl_easy *data, bool *done)
 #ifdef HAVE_LDAP_URL_PARSE
   rc = ldap_url_parse(data->state.url, &ludp);
 #else
-  rc = _ldap_url_parse(data, conn, &ludp);
+  rc = ldap_url_parse_low(data, conn, &ludp);
 #endif
   if(rc) {
     failf(data, "Bad LDAP URL: %s", ldap_err2string((curl_ldap_num_t)rc));
@@ -728,7 +728,7 @@ quit:
 }
 
 #ifdef DEBUG_LDAP
-static void _ldap_trace(const char *fmt, ...)
+static void ldap_trace_low(const char *fmt, ...)
 {
   static int do_trace = -1;
   va_list args;
@@ -795,8 +795,9 @@ static size_t num_entries(const char *s)
  *
  * Defined in RFC4516 section 2.
  */
-static int _ldap_url_parse2(struct Curl_easy *data,
-                            const struct connectdata *conn, LDAPURLDesc *ludp)
+static int ldap_url_parse2_low(struct Curl_easy *data,
+                               const struct connectdata *conn,
+                               LDAPURLDesc *ludp)
 {
   int rc = LDAP_SUCCESS;
   char *p;
@@ -999,9 +1000,9 @@ quit:
   return rc;
 }
 
-static int _ldap_url_parse(struct Curl_easy *data,
-                           const struct connectdata *conn,
-                           LDAPURLDesc **ludpp)
+static int ldap_url_parse_low(struct Curl_easy *data,
+                              const struct connectdata *conn,
+                              LDAPURLDesc **ludpp)
 {
   LDAPURLDesc *ludp = calloc(1, sizeof(*ludp));
   int rc;
@@ -1010,16 +1011,16 @@ static int _ldap_url_parse(struct Curl_easy *data,
   if(!ludp)
     return LDAP_NO_MEMORY;
 
-  rc = _ldap_url_parse2(data, conn, ludp);
+  rc = ldap_url_parse2_low(data, conn, ludp);
   if(rc != LDAP_SUCCESS) {
-    _ldap_free_urldesc(ludp);
+    ldap_free_urldesc_low(ludp);
     ludp = NULL;
   }
   *ludpp = ludp;
   return rc;
 }
 
-static void _ldap_free_urldesc(LDAPURLDesc *ludp)
+static void ldap_free_urldesc_low(LDAPURLDesc *ludp)
 {
   if(!ludp)
     return;